ask... you can ask the top tier, but that doesn't usually work. Ask in the middle ranks or those just above you in rank. Ask outside your field... you're marketing so you could stand a writer or two to do a guest post. And/or even one of your clients if they can write.
What niche is your blog in? Knowing that might help us think of people that we can refer you to (I know a few bloggers who are always looking for guest posting gigs, but they operate in very specific niches). You might also just consider sending an e-mail to the bloggers you like the most and asking them to do a guest post on your site as well.
It's not about advertising but about getting guest authors, people willing to write articles for this blog. Exposure is the key word to achieve results, I must say. Offering exposure to novice writers might be the way to go, but explain how can they benefit from writing on, whether traffic your blog receives or why they need to gain exposure. Novice writers often need to reference sample articles or published works so while expert writers point their portential clients to Ezine, novice writers can point them to your blog. Now, if you are looking for writers in your same rank or above, that's another story that might be harder to achieve, unless you have a very popular blog
Hold a guest blogger contest for 3 or 4 entrants. Whichever guest blogger brings the most traffic + comments or something else in a month gets the prize. May create some adjudication issues/fraud concerns though.
Advertising in your blog will target your audience, you can make a page that explains the benefit of writing a guest post and a form where you can submit your idea.